As technique of transmitting an electric signal between two circuits to which electric signals having different electric potentials are inputted, respectively, technique using a photocoupler has been known. The photocoupler is provided with a light-emitting element, such as a light emitting diode, and a light-receiving element, such as a phototransistor, and by converting an inputted electric signal into light by the light-emitting element, as well as by returning the light into an electric signal by the light-receiving element, the electric signal is transmitted.
Moreover, a technique in which electric signals are transmitted by inductively coupling two coils with each other has been developed. For example, Patent Document 1 (Japanese Patent Application Laid-Open Publication No. 2009-302418) discloses a circuit device provided with a first coil, a first insulating layer and a second coil.
Furthermore, Patent Document 2 (Japanese Patent Application Laid-Open Publication No. 2003-309184) discloses a composite module in which a coil and a capacitor are formed on the same substrate so that a plurality of stacked coil patterns are provided.
In addition, Patent Document 3 (Japanese Patent Application Laid-Open Publication No. 2009-141011), Patent Document 4 (Japanese Patent Application Laid-Open Publication No. 2004-311655) and Patent Document 5 (Japanese Patent Application Laid-Open Publication No. 2004-281838) respectively disclose a seal ring, a metal fence and a guard ring.